The present invention relates to an optical analyzing apparatus having an optical system including a light source portion, a cell portion and a detector portion.
The optical analyzing apparatus such as, for example, an infrared gas analyzing apparatus, has been used for analyzing various gases by utilizing the difference in infrared absorption between the test gas and a reference gas. As shown in FIG. 1, a typical infrared gas analyzing apparatus comprises a light source portion which includes a light source chamber 1, a chopper chamber 18 containing a chopper plate 3 rotated by a motor 4 and a light dividing chamber 5, a cell portion including a reference cell 6 and a sample cell 7, and a detector portion 8 including a pair of detector chambers 8A and 8B.
It is possible to use two light sources rather than the single source and light divider of FIG. 1. However, if two light sources are used, an unbalance between the light sources may be a problem, causing a drift of the null point of the system. On the other hand, there is no such drift problem in the single light source type due to the fact that it uses only one source, the infrared light from which is divided into two beams in the light dividing chamber. Therefore, the single light source type gas analyzer has been widely used.
The light divider 5 has an inlet window facing the light source chamber 2 sealed with a sealing plate 9 of an infrared transparent material and also has a pair of outlet windows which are sealed by plates 10 and 11 of an infrared transparent material, respectively. Light passages connecting the inlet window and the respective outlet windows have circular cross sections of the same diameter. The passages are filled with a gas such as nitrogen gas which does not absorb the infrared ray. If the sample gas contains an interfering gas component which will absorb the infrared ray at a wavelength to be absorbed by an object gas component, the passages can be filled with the interferring gas.
The two beams are guided through the passages into the cell portion comprising a reference cell 6 and a measuring cell 7. One of the beams passes through the reference cell 6 as a reference beam and the other passes through the measuring cell 7 as a measuring beam. Opposite ends of the reference cell 6 are sealed with light transparent windows 14 and 15 and, as in the light divider 5, the cell 6 is filled with a gas such as pure nitrogen gas which does not absorb the intended wavelength of the infrared ray. The measuring cell 7 is also sealed at opposite ends with light transparent windows 12 and 13 and is provided at the upstream side thereof with a gas inlet port 7A for in introducing the measuring or sample gas and at the downstream side thereof with an outlet port 7B to establish a flow of the measuring gas containing the gas component to be analyzed. The measuring beam is absorbed by the gas component, the amount of absorption being dependent upon the concentration thereof.
The beams passed through the respective cells are introduced into the detector portion. The detector portion is a gas filled detector 8 which comprises detecting chambers 8A and 8B sealed with light transparent windows 16, 17 and filled with a pure gas of the same kind as the gas component of the sample gas which is to be analyzed, so that the detector chambers 8A and 8B are heated to different temperatures according to intensities of the measuring beam and the reference beam passed thereto, respectively. The chambers 8A and 8B are communicated with each other by a communication portion 8C in which a pair of heat-sensitive elements 8D and 8E are disposed. The elements 8D and 8E, together with a pair of resistors (not shown) constitute a bridge circuit which is heated to a temperature higher than the ambient temperature by supplying a d.c. current therethrough. When the gases in the chambers 8A and 8B are heated to different temperatures according to the different intensities of the beams, a flow of the gas occurs through the communicating portion 8C from the chamber 8B to 8A because the gas in the chamber 8B is heated to a higher temperature than that in chamber 8A. The gas flow is converted by the elements 8D and 8E into an electric signal indicative of the amount of the particular gas component contained in the sample gas.
FIG. 2A shows in cross section the light source portion of FIG. 1 in more detail and FIG. 2B is a cross section taken along IIB--IIB of FIG. 2A. In FIG. 2A the chopper plate 3 of FIG. 1 is omitted for convenience in explanation.
In FIG. 2A, the opening of the light source chamber 1 faces the sealing plate 9 in the inlet 19 of the light divider 5. The inside surface of the light source chamber 1 behind the light source 2 is formed with a plurality of conical mirrors K1 and K2 which effectively reflect the light emitted from the rear side of the light source 2 back to the light divider 5.
The light divider 5 is formed with a pair of straight passages 60 and 61, each having one end connected together at the inlet 19 and the other ends of which form separate outlets 21 and 22 of the divider 5, respectively, forming a generally V-shaped space. The light passages 60 and 61 have the same diameter D and optical axis A1 and A2, respectively. A cross point P of the axes A.sub.1 and A.sub.2 corresponds to the center of the sealing plate 9.
In order to increase the amont of light emitted from the light source portion and introduced into the divider 5, to thereby improve the efficiency of the analyzer, it is necessary to either raise the temperature of the light source 2 or increase the light emitting area of the light source 2, according to Stefan-Boltzmann's law. Raising the light source temperature may cause the life of the light source to be shortened. Therefore, it is preferable to enlarge the light source. However, even if the light emitting area of the light source 2 is enlarged, the effective light emitted by the enlarged light source and guided into the light passages 60 and 61 may not be increased proportionally to the increase of the light emitting area of the light source. In other words, the effective light cannot be increased proportionally to the electric power consumed, resulting in inefficiency. Therefore, it is highly desirable to provide a more efficient way of increasing the effective light.
A further disadvantage of the conventional infrared gas analyzer can be understood from FIG. 3.
In FIG. 3, the light source portion including the chopper mechanism 3, 4, 18, and the light source chamber 1, the light divider 5, the measuring cell portion including the reference cell 6 and the measuring cell 7 and the detector portion 8 are independently mounted on a base plate 23. The divider 5 to which is mounted the light source chamber 1 and the chopper mechanism is fixed to a supporting plate 24 by suitable means (not shown) and the supporting plate 24 is fixedly secured to the base plate 23 by means of mounting screws 27.
The reference cell 6 and the measuring cell 7 are supported in parallel between a supporting plate 28 and a pair of supporting members 25 and 26 by screws 35 and 36 and the supporting members are fixedly secured to the base plate 23 by screws 31, 32, 33 and 34. Finally, the detector portion 8 is suitably supported by a supporting member 29 which is fixedly secured to the base plate 23 by screws 37, 38, 39 and 40.
In order to perform the analysis effectively, it is necessary to align the optical axes of the light divider 5, the cells 6 and 7 and the detector 8. However, with this arrangement of the functional components, it is very difficult to obtain an exact alignment of the components due to the independent securings for each. Furthermore, even if the exact alignment is achieved, the components may be disposed due, for instance, to temperature variations causing the analysis to be inaccurate and, therefore, the components have to be realigned.